The invention relates to an apparatus for heating gases, particularly air, with a heating unit having a mounting part, at least one PTC component, at least one insulating frame part surrounding the latter, at least one contact plate and at least one insulating support, with the PTC part, surrounded by the frame part, being placed in the mounting part and a contact plate rests on at least one flat side and is covered by an insulating support.
Such heating apparatuses have been be known in the form of wire heaters and tubular heaters. In the case of gas heaters the heating wires are lead freely over long distances, so that air and a gas can flow between them and can be heated. In the case of tubular heaters the heating wire placed inside a tube is embedded in an insulating material. To heat air or gas, the tubes must be provided with heat emission lamellas. This is in part brought about in that the lamellas are constructed in one piece with the tube jacket. Alternatively use, is made of slotted tubes, which are pressed by expansion against mounted lamellas, so as in this way to provide a firm connection. The actual tubular heater being inserted in the expanded, slotted tube. The winding round tubular heaters in part takes place by coiling. According to another construction the tubular heater is formed by profile sheet metal strips, which are interconnected by folded seams and as ribs extending longitudinally of the tubular heater project laterally therefrom. As in this case the ribs are not at right angles to the tubular heater axis, only an unsatisfactory heat emission is obtained. According to another tubular heater construction for air heating purposes, lamellas extending at right angles to its axis are welded to an outer jacket, which is subsequently pressed onto a ceramic part containing the heating wires by pressing in or firmly rolling. It has finally also been proposed to surround the tubular heater with a coating shaped in one piece with the ribs.
For some time now self-stabilizing heaters have been provided with PTC components as the heat producing element. Unlike in the case of resistance heaters, which produce the heat as a result of the power applied and their substantially constant resistance, in the case of PTC components the production of heat is dependent on their temperature, dropping with higher temperature and is consequently dependent on how effectively the initially produced heat is removed. PTC components have hitherto been used for heating liquids or solids, such as soldering irons and curlers.
The aim the invention is to provide an apparatus for heating gases, particularly air, of the aforementioned type with a PTC component as the heating element, which ensures an effective emission of heat to the air or a gas surrounding the apparatus, so that an adequate heating power is obtained.
According to the invention, an apparatus of the aforementioned type is characterized in that heat emission lamellas are mounted in clamping manner on said heating unit.
As a result of the inventive construction a heating unit based on a PTC component can be provided with heat emission lamellas, which are on the one hand reliably secured so as to ensure an adequate heat removal from the actual heating unit to the heat emission lamellas and from there to the surrounding air, while at the same time adequately compensating dimensional changes occurring as a result of the temperature changes, so that permanently a firm seating of the heat emission lamellas on the heating unit is ensured. This is further improved in that the compressive force of the heating unit against the heat emission lamellas is naturally reinforced on raising the temperature. In a preferred development, the inventive apparatus for heating gases is constructed in such a way that the lamellas have openings surrounding the heating unit and which are bounded by two facing tongues bent out of the plane of the lamellas and which have a spacing in their connection area with respect to the lamella bodies corresponding to the height of the heating unit, while the internal spacing of the ends of the tongues is smaller than the height of the heating unit. This construction leads to a simple and preferred clamp fit, which ensures the aforementioned advantages.
According to a further development, the lamellas have grooves or creases, which are in particular directed at right angles to the tongues. The construction stabilizes the heat emission lamellas and, in particular, prevents a fluttering or oscillating thereof when air passes through, particularly if it is forced through the lamellas by convection. The prevention of lamellas oscillation avoids the noise produced as a result thereof.
In a preferred manner, the mounting part is constructed as a U-profile. On the insulating support, which is generally made from relatively break-sensitive material, such as metal oxides, are placed cover plates, so that the tongues of the lamellas on the one hand engage directly on said cover plates and on the other hand on the web of the U-profile and the two press against one another, accompanied by the interposing of insulating plates and the PTC component. The lamellas, mounting part and cover plate are preferably made from aluminium or an aluminium alloy, such as in particular spring hard aluminium with a hardness of F28 and with thermal stability of over 400.degree. C.
PTC components are preferably surrounded on their narrow sides by a frame part, which has transverse webs, which keeps the PTC components spaced. The insulating support is preferably formed from individual insulating plates, whose width corresponds to the frame width and whose length substantially corresponds to that of the PTC components, plus the transverse web width of the frame part, so that the insulating support parts are longitudinally linked to one another. The coverage of the cover plates substantially corresponds to the insulating supports. As a result of this subdivision of the cover plates and insulating supports in accordance with the PTC components, a good pressing action is achieved by the pressed on lamellas over the length of the individual portions.
According to a preferred development, the apparatus has a holding part for PTC components with an insulating frame and at least one contact plate, in which the latter is firmly connected to the insulating frame. In order to ensure a reliable hold of the PTC components during handling, it is not sufficient to have an insulating frame surrounding the narrow sides of the PTC components because, even if a substrate is held against the same from below, e.g. in the form of a contact plate, there is a risk of the insulating frame and substrates sliding relative to one another, so that once again a single PTC component can fall out of the frame. According to this further development, the contact plate and the insulating frame are firmly interconnected. The term firmly interconnected here means that they cannot be detached without considerable effort and in particular that they cannot be loosened from one another by chance or slide relative to one another. It would fundamentally also be possible to use a screw coupling. However, preferably the contact plate is riveted in the vicinity of one of its ends to the insulating frame. The firmly fitted contact plate is positioned on one side of the frame, so that the individual PTC components can be inserted in the frame part from the opposite side and are prevented from dropping out by the contact plate. The further contact element, such as a further plate or a profile contact body with a U-shaped cross-section can then be placed on the side of the frame and the inserted PTC components facing the contact plate firmly connected to the frame. It is then possible to position further cover elements, such as stable cover plates or the like which protect the insulating member up to the time of further assembly, namely the optional placing of insulating plates on the contact plate. According to a further development, of the holding part, a connecting tongue is riveted to the contact plate and/or a contact tongue is constructed in one piece with the contact plate. If the contact plate is already firmly connected to the insulating frame, it is then also apropriate to construct in one piece therewith a connecting tongue, namely, that connected to the contact plate and/or to firmly connect it, e.g. by riveting to the insulating frame.
If a relative pivoting of frame and contact plate could also be prevented by two rivets, which are either juxtaposed in one end region or are in each case located at one end region, then it is advantageous to prevent pivoting of that end of the contact plate which is not firmly connected to the insulating frame and also to prevent any bending out of its plane, but not to completely fix the same, so that the end can perform compensating movements, e.g. under compressive forces and temperature changes. In order to achieve this, according to another preferred development, on the end of the insulating frame opposite to the fixed connection between the contact plate and the insulating frame is formed a clip raised out of the plane thereof and which engages over the contact plate end opposite to the fixing point and in particular the contact plate is free between its end region.
In order to prevent a giving way or yielding of the contact plate under compressive forces exerted during the further assembly of a PTC heater, to ensure a good heat transfer and therefore to obtain the same, according to a preferred development the contact plate is made from flexible sheeting. It is then preferred that the contact plate is bent in convex manner and pretensioned with respect to the frame part. As a result in the case of locally exerted forces, i.e. not exerted over the entire length of the frame and contact plate and which essentially act in the central region, an adequate pressing action is obtained and therefore a sufficiently good contact between the contact plate and the PTC components over the entire length.
According to a further development in the vicinity of the fixing point ofn the frame side facing the contact plate are provided cams extending out of the plane thereof. It is thus possible to prevent an axial displacement of insulating plates resting on the contact plate side remote from the frame. According to another construction the frame has transverse webs. As a result the individual PTC components can be individually grasped and received in recesses within the frame part.